Qt 5.12 build breaks with gcc 4.8 compiler

/home/ghguest/src/qtbase/src/corelib/global/qendian.cpp:41:0:
/home/ghguest/src/qtbase/src/corelib/global/qendian.h:165:61: error:
redeclaration 'constexpr T qbswap(T) [with T = qfloat16]' differs in
'constexpr'
template <> inline qfloat16 qbswap<qfloat16>(qfloat16 source)
^
/home/ghguest/src/qtbase/src/corelib/global/qendian.h:96:42: error: from
previous declaration 'constexpr T qbswap(T) [with T = qfloat16]'
template <typename T> Q_DECL_CONSTEXPR T qbswap(T source);
^
/home/ghguest/src/qtbase/src/corelib/global/qendian.h:170:52: error:
redeclaration 'constexpr T qbswap(T) [with T = float]' differs in 'constexpr'
template <> inline float qbswap<float>(float source)
^
/home/ghguest/src/qtbase/src/corelib/global/qendian.h:96:42: error: from
previous declaration 'constexpr T qbswap(T) [with T = float]'
template <typename T> Q_DECL_CONSTEXPR T qbswap(T source);
^
/home/ghguest/src/qtbase/src/corelib/global/qendian.h:175:55: error:
redeclaration 'constexpr T qbswap(T) [with T = double]' differs in 'constexpr'
template <> inline double qbswap<double>(double source)